With enhancement of degree of integration and formation of more multi-layer interconnections in the semiconductor devices, storage capacities of memory devices have been greatly increased. Although this is supported by an advancement in the fine process technology, increase of chip sizes and increase of production steps due to the fine process technology are brought about in spite of the formation of more multi-layer interconnections, whereby rising cost of chips is created. Under such circumstances, a chemical mechanical polishing technique has been introduced into polishing of process films or the like and paid attention. By the adoption of such a chemical mechanical polishing technique, a great number of the fine process technologies, such as flattening, have been embodied.
As one of such fine process technologies, shallow trench isolation, namely, so-called STI technology is known. In this STI technology, chemical mechanical polishing is carried out in order to remove an excess of an insulating layer formed on a wafer substrate. In the chemical mechanical polishing step, flatness of the polished surface is important, and on this account, various polishing agents have been studied.
For example, Japanese Patent Laid-Open Publication No. 326469/1993 and Japanese Patent Laid-Open Publication No. 270402/1997 disclose that application of an aqueous dispersion using ceria as abrasives in the chemical mechanical polishing step of STI makes it possible to enhance a removal rate and to obtain a polished surface having relatively less polishing scratches.
With developments of finer and more multi-layer interconnections of semiconductor devices, further improvement of yield or throughput of the semiconductor devices has been required in recent years. With such requirement, it has been desired to polish at a high removal rate and to provide polished surfaces substantially suffering no polishing scratches after the chemical mechanical polishing.
With respect to decrease of polishing scratches on the polished surfaces, it has been reported that polishing agents which are prepared using dispersing agents, such as polycarboxylic acid based high-molecular-weight compounds containing ammonium acrylate, in combination with surfactants (additives), such as chitosan acetate (Japanese Patent Laid-Open Publication No. 109809/2000), dodecylamine (Japanese Patent Laid-Open Publication No. 7061/2001) and polyvinyl pyrrolidone (Japanese Patent Laid-Open Publication No. 185514/2001), are effective. In such polishing agents, however, from the viewpoint of dispersibility and prevention of the sedimentation of cerium oxide particles in the slurry and decrease of polishing scratches, the amount of the dispersing agents is preferably not less than 0.01 parts by weight and not more than 2.0 parts by weight, and the amount of the surfactants is preferably not less than 0.01 parts by weight and not more than 1000 parts by weight, based on 100 parts by weight of cerium oxide particles.
U.S. Pat. No. 6,443,811 discloses a polishing agent comprising less than 5 wt % abrasive cerium oxide particles and up to about the critical micelle concentration of a cationic surfactant. The Patent also discloses that this polishing agent may contain 2 to 6 wt % anionic surfactant. However, the Patent discloses no specific examples of the anionic surfactant, and exemplifies only an ammonium or pyridinium compound having alkyl of 6 to 18 carbon atoms as the cationic surfactant.
Japanese Patent Laid-Open Publication No. 190458/2002 discloses a polishing agent comprising ceria and nitrogen atom-containing surfactant. The document also discloses that this polishing agent may further comprises a dispersing agent, such as a high-molecular-weight polyacrylic acid. In the document, however, there is no specific disclosure on the combination of the nitrogen atom-containing surfactant with the dispersing agent.
By the use of such technique, however, the removal rate is lowered though there is observed an effect of decreasing the polishing scratches, and hence improvement of throughput has not been accomplished yet.